U.S. Pat. No. 3,653,083 discloses an inflatable bed pad with passages which expand and collapse as they are inflated and deflated. Perforations which are formed in the top wall of the pad and which communicate with the passages allow air to escape upwardly through a foam cushion or sheet extending over the pad. Inflating air is introduced at one end of each passage by means of an air pressure line connected to the pad and a valve controls the flow of air so that one passage is inflated as the other is allowed to deflate, such deflation occurring because of the upward flow of air through the perforations of the passage to which the air supply is temporarily interrupted. As a result, such alternating inflation and deflation of the passages produces a "rippling effect" which stimulates peripheral circulation and relieves localization of pressure for a patient lying upon the pad and its foam cushion. Also, because air escapes from the perforations and passes upwardly through the foam cushion, a gentle drying effect is produced which prevents or reduces skin maceration caused by trapped perspiration. The total effects are an increase in patient comfort and a substantial elimination in the formation of decubitus ulcers previously experienced by bedridden patients.
Other U.S. Pat. Nos. reflecting the state of the prior art are 2,998,817 (an inflatable mattress having two arrangements of transverse cells, each of the cells being simultaneously inflated (or deflated) from its opposite ends), 95,848 (an air bed which, in one embodiment has one or more tubes supplied with air from one end, closed at the opposite end, and provided with perforations to discharge air for cooling and ventilating purposes), 3,486,177 (vertilated cushion), 3,266,064 (ventilated mattress and box spring combination), 3,394,415 (alternating pressure pad), 3,199,124 (alternating pressure mattress), 1,772,310 (variable pressure mattress), 2,345,073 (an apparatus including a distribution valve for controlling the air flow for therapeutic devices), 3,908,642 (a distributor and associated elements for directing pulsating air into and out of casts), 3,919,730 (inflatable body support), 3,446,203 (pneumatic cushion), 3,462,778 (inflatable mattress), and 3,467,081 (inflatable mattress).